This invention relates to electronic ballasts for gas discharge lamps, particularly to electronic ballasts each of which being operable to power plural parallel-connected lamps.
For a description of pertinent prior art, reference is made to U.S. Pat. No. 4,677,345 to Nilssen; which patent issued from a Division of application Ser. No. 06/178,107 filed Aug. 14, 1980; which application is an in-part progenitor of instant application.
Otherwise, reference is made to the following U.S. Patents: U.S. Pat. No. 3,263,122 to Genuit; U.S. Pat. No. 3,320,510 to Locklair; U.S. Pat. No. 3,996,493 to Davenport et el.; U.S. Pat. No. 4,100,476 to Ghiringhelli; U.S. Pat. No. 4,262,327 to Kovacik et al.; U.S. Pat. No. 4,370,600 to Zansky; U.S. Pat. No. 4,392,087 to Zansky; U.S. Pat. No. 4,398,126 to Zuchtriegel; U.S. Pat. No. 4,634,932 to Nilssen; and U.S. Pat. No. 4,857,806 to Nilssen.
A main object of the present invention is that of providing cost-effective ballasting means for gas discharge lamps.
This as well as other objects, features and advantages of the present invention will become apparent from the following description and claims.
In an electronic ballast, a half-bridge inverter is powered from a DC voltage and provides a 40 kHz squarewave inverter output voltage. The DC voltage is obtained via a pre-converter with a control input operative to permit control of the magnitude of the DC voltage.
The 40 kHz squarewave inverter output voltage is applied across a series-resonant L-C circuit, thereby establishing a 40 kHz sinusoidal voltage across the L-C circuit""s tank capacitor. By controlling the symmetry of the squarewave voltage, the magnitude of the 40 kHz sinusoidal voltage is regulated to be appropriate to instant-starting a gas discharge lamp.
Each of several instant-start fluorescent lamps is series-connected with a capacitor, such as to form several lamp-capacitor series-combinations, each of which is connected across the tank capacitor, thereby to be properly ignited and powered from the magnitude-controlled 40 kHz sinusoidal voltage.
To attain imroved efficiency of operation, after the lamps have all ignited, the magnitude of the 40 kHz sinusoidal voltage is reduced, thereby minimizing the amount of reactive power having to be handled by the resonant L-C circuit.